1. Field of the Invention
The present invention relates to an optical pickup used for an optical video disc, compact disc and the like, a supporting method for it, and a method for assembling it.
2. Description of the Related Art
A conventional optical pickup is described hereinafter. FIG. 11 is a plan view of a conventional optical pickup; FIG. 12(a) is a sectional view of the optical pickup of FIG. 11 taken along line XII(a)--XII(a); and FIG. 12(b) is a sectional view of the optical pickup of FIG. 11 taken along line XII(b)--XII(b).
Referring to the figures, there is shown an objective lens holder tube 1 on which an objective lens 4 for focusing laser beam 3 onto an optical disc 2 is secured with adhesives or the like. In addition, secured on the objective lens holder tube 1 with adhesives or the like are a focusing coil 5 for operation in the focusing direction (direction perpendicular to the plane of the optical disc 2) and a tracking coil 6 for operation in the tracking direction (radial direction of the optical disc 2 indicated by an arrow T). There are also shown permanent magnets 7a and 7b for constituting a magnetic circuit which drives the objective lens holding tube 1 in the focusing and tracking directions. The magnets are magnetized to the N pole at the objective lens 4 side and to the S pole at the opposite side. The optical disc 2 is rotatably driven by a spindle motor or the like (not shown).
There is provided a conductive linear elastic member 8 for holding the objective lens holder tube 1 at the neutral position, and also supplying electric power to the focusing coil 5 and the tracking coil 6. This member is constituted by a non-magnetic material so that the magnets 7a and 7b do not exert magnetic attractive force. A junction board 9 secured at each end of the objective lens holder tube 1 with means such as adhesives is a junction board for supplying electric power to the focusing coil 5 and the tracking coil 6 from the linear elastic members 8, one end of which is soldered so that respective patterns on the junction board 9 conducts to individual linear elastic members 8.
A suspension holder 10 is secured at one end with an FPC (not shown) for supplying electric power with adhesives or the like, and at one end reverse to the objective lens 4 with the linear elastic members 8 by soldering. In addition, the suspension holder 10 is secured on a carriage 11 movable from an inner periphery to an outer periphery of the optical disc 2. A damping member 12 is used for suppressing Q value of the primary resonance which a system constituted by an optical moving section (actuator) including the objective lens holder tube 1 and the linear elastic members 8 has. A material with low viscosity such as silicon gel is used for the damping member 12.
The optical pickup arranged as above is described for its operation. First, electric power is supplied from a power supply to the focus coil 5 and the tracking coil 6 through the FPC (not shown), the linear elastic members 8, and the junction board 9. Currents flowing through the focusing coil 5 and the tracking coil 6 exert electromagnetic forces on the focusing coil 5 and the tracking coil 6 according to the Fleming's left hand rule under the influence of the magnetic fields generated by the permanent magnets 7a and 7b so that the movable section (actuator) of the optical pickup including the objective lens holder tube 1 can be driven. The direction and magnitude of the current flowing through each coil are controlled to adjust the position of the objective lens 4, whereby an optical spot which is a converged laser beam 3 is controlled to be constantly focused on the optical disk 2 and to follow a track of optical pits (fine tracking). In addition, when supply of the electrical power is stopped, the objective lens is always returned to the neutral position in the focusing and tracking directions by the spring force of the linear elastic members 8.
An optical unit 13 has a light emitting element and a light receiving element for the laser beam 3. The laser beam 3 emitted from an optical unit 13 passes through an optical component 13a constituting a hologram, is totally reflected on the surface of a multi-layer coated riser mirror 14, converged by the objective lens 4, and images an optical spot on the optical disc 2. Oppositely, the laser beam 3 reflected from the optical disc 2 is totally reflected on the riser mirror 14, passes through the optical component 13a constituting a hologram, and is collected on the light receiving element (not shown). The objective lens 4 is focused on the optical disc 2, and controlled to follow the track of the optical pits based on a received light signal converted into an electrical signal by the light receiving element (not shown).
Now, a method for assembling the optical pickup as described above is described. FIGS. 13(a) and 13(b) are views illustrating the step of connecting the junction board a and the linear elastic members 8; FIGS. 14(a) and 14(b) are views illustrating the step of combining the suspension holder 10 and the linear elastic members 8; and FIGS. 15(a) and 15(b) are views illustrating the step of completing the connection of the linear elastic members.
First, referring to FIGS. 13(a) and 13(b), the movable section (actuator) including the objective lens holder tube 1 is mounted on a jig 15. Then, the suspension holder 10 on which the FPC (not shown) for supplying electric power is bonded with means such as adhesives is mounted on a jig 16. Furthermore, the linear elastic members 8 are mounted on a jig 17 with means such as air suction so that four linear elastic members 8 are parallel to each other.
In this initial stage, the jig 16 is retracted in the direction of W to a position where the suspension holder 8 does not come into contact with the linear elastic members 8 and the jig 17 is moved toward the movable section (actuator) including the objective lens holder tube 1 to a predetermined position. In this state, the linear elastic members 8 are secured on portions of the junction board 9 at the movable section (actuator) side at four positions with solder.
Then, holding of the linear elastic members 8 is released from the jig 17. In this state, the linear elastic members 8 are secured on the junction board 9 of the movable section (actuator), so that they would not drop.
Then, referring to FIGS. 14(a) and 14(b), the jig 16 is moved in the direction of W, and set at a predetermined position. In this case, the tips of the linear elastic members 8 pass through small holes 10a drilled through the suspension holder 10.
Then, referring to FIGS. 15(a) and 15(b), the optical pickup is assembled by soldering the linear elastic members 8 passed through the small holes 10a in the suspension holder 10, and filling conical spaces with dumping members 12. FIG. 11 shows a state where the optical pickup thus assembled is mounted on the carriage 11. In the figure, four parallel linear elastic members 8 support between the junction board 9 and the suspension holder 10.
In the optical disc device using the conventional optical pickup as described above, an optical pickup which can be easily and precisely assembled and does not cause vibration is demanded as the optical disc device is enhanced for its performance, improved for its access speed, and reduced for its size (thinned).
However, in the optical pickup with the above arrangement, the position of the objective lens 4 (substantially the center of gravity of the entire drive section) is spaced away from the drive point (the focusing coil 5 and the tracking coil 6). Thus, there tends to arise vibration in pitching mode (plane vibration, secondary resonance of the focus system) or yawing mode (eccentricity, secondary resonance of the tracking system) of the linear elastic member 8. Therefore, since it is necessary to match the position of center of gravity of the movable section including the objective lens holder tube 1 and the position of the drive point in the order of several .mu.m to suppress the vibration, it is necessary to conduct the production in a very severe tolerance.
In addition, since variation of the center of gravity in manufacturing induces vibration of the linear elastic member 8 in the pitching or yawing mode, impediment on control may arise when the phase of vibration occurs.
To solve the above problems, there has been proposed a wire suspension structure movable in the tracking, focusing and tangential direction (Japanese Utility Model Unexamined Publication No. 61-48424) and a structure for dampedly supporting wires (Japanese Utility Model Unexamined Publication No. 62-120425). However, any of them cannot suppress the secondary resonance of the focusing and tracking systems.
The present invention is intended to solve the above conventional problems, and to provide an optical pickup not causing vibration, a method for supporting the optical pickup, and a method for assembling the optical pickup.